The present invention relates to glass fibre-reinforced polyamides and the use of the latter for thermoforming.
The thermoforming of thermoplastic semi-finished products has become increasingly important in recent years. Not least, the possibility of being able to develop prototypes quickly offers advantages compared to the more expensive rival processes such as injection moulding processes. Constantly improved thermoplastic materials enable the output to be increased with modern machinery and tools, combined at the same time with improved precision of the mouldings (Kunststoff Handbuch 3/4 xe2x80x9cPolyamidexe2x80x9d, Hanser Verlag, Munich, Vienna).
Polyamides, and in the present context in particular reinforced polyamides from the group comprising partially crystalline thermoplastic materials, were hitherto largely excluded from thermoforming applications (Thermoformen in der Praxis, p. 45 ff, Hanser Verlag, Munich, Vienna). The very narrow processing window of this class of materials, which allowed forming to be carried out only just below the crystalline melting point, and the insufficient melt stabilities of these polymeric materials as a result of the low melt viscosities, enabled semi-finished products (sheets) produced therefrom to be formed only into very flat mouldings with low stretch/draw ratios and reduced shaping sharpness.
The thermoforming of films, which is often referred to as deep drawing, is known for polyamide films (single-layer. multi-layer. co-extruded or laminated) (Verpacken mit Kunststoffen, Hanser Verlag, Munich, Vienna). The person skilled in the art refers to films having a thickness of less than 1500 xcexcm as suitable for deep drawing applications (Thermoformen, Hanser Verlag, Munich, Vienna, 1999).
The object therefore existed of providing a reinforced polyamide from which thermoplastic semi-finished products can be then produced having a material thickness of greater then 1.5 mm, from which in turn mouldings can be produced by thermoforming having a high degree of forming and a good shaping sharpness.
It has now surprisingly been found that polymeric materials from the class of materials of pseudoplastic reinforced polyamides, such as are described for example in EP-A 0 685 528, with a viscosity behaviour according to the invention, are extremely suitable for thermoforming. Degrees of forming can be obtained that are significantly better than those achievable with hitherto known materials. The materials also have a large forming temperature range.
These moulding compositions are characterised by their clearly defined pseudoplastic behaviour compared to standard polyamides. In other words, these moulding compositions have a significantly higher viscosity at low shear velocities compared to standard polyamides and comparably high viscosities at high shear velocities. This pseudoviscosity is achieved via an increased degree of branching of these polyamides. This can be achieved on the one hand in the primary condensation in a so-called VC tube, or also in a subsequent compounding.
The reinforcement of polyamides is carried out in a known manner by incorporating for example glass fibres or mineral fillers in the polyamide melt, for example from an extruder.
The present invention accordingly provides reinforced polyamide moulding compositions whose viscosity at a shear velocity of 10 sxe2x88x921 is greater than 1000 Pas and at a shear velocity of 1000 sxe2x88x921 is less than 300 Pas, at a processing temperature of 40 to 80xc2x0 C. above the melting point of the relevant moulding composition.
Reinforced polyamide moulding compositions are preferred whose viscosity at a shear velocity of 10 sxe2x88x921 is greater than 1500 Pas and at a shear velocity of 1000 sxe2x88x921 is less than 280 Pas, at a processing temperature of 40-80xc2x0 C. above the melting point of the relevant moulding composition.
The invention also provides for the use of these moulding compositions according to the invention for thermoforming.
It is preferred to use moulding compositions containing:
A) 98 to 41 parts by weight of thermoplastic partially crystalline polyamide and
B) 2 to 50 parts by weight of reinforcing materials
C) 0.1 to 4 parts by weight of branching additives and/or additives raising the molecular weight, for example diepoxide
D) 0 to 5 parts by weight of further additives, for example processing additives for thermoforming, colouring agents, carbon black.
the sum of the parts by weight of A, B, C and D totalling 100,
for thermoforming.
It is particularly preferred to use moulding compositions containing
A) 67 to 85 parts by weight of thermoplastic partially crystalline polyamide and
B) 15 to 30 parts by weight of reinforcing materials
C) 0.2 to 1 part by weight of branching additives and/or additives raising the molecular weight, for example diepoxide
D) 0.1 to 2 parts by weight of further additives, for example processing additives for thermoforming, colouring agents, carbon black,
the sum of the parts by weight of A, B, C and D totalling 100,
for thermoforming.
The application also provides thermoformed moulded bodies obtainable from the aforedescribed used moulding compositions.
Partially crystalline polyamides (PA), preferably PA 6, PA 66, PA 46, PA 610, PA 6/6T or partially crystalline copolyamides or mixtures based on these components are suitable as thermoplastic polyamide A).
The class of substances comprising polyamides is described in Kunststoff Handbuch 3/4 xe2x80x9cPolyamidexe2x80x9d, Hanser Verlag, Munich, Vienna. This relates in particular to the production of the base resins (Chapter 2.1), as well as their modification (Chapter 2.3) and their reinforcement (Chapter 2.4).
A large number of procedures are known for producing polyamides, different monomer building blocks, various chain regulators for achieving a desired molecular weight or also monomers with reactive groups for subsequently intended post-treatment procedures being used depending on the desired end product.
The technically relevant processes for producing polyamides take place without exception via polycondensation in the melt. The hydrolytic polymerization of lactams is also understood as polycondensation in this context.
Preferred polyamides for the moulding compositions according to the invention are partially crystalline polyamides that can be produced starting from diamines and dicarboxylic acids and/or lactams having at least five ring members or corresponding amino acids.
Suitable starting products are preferably aliphatic dicarboxylic acids such as adipic acid, 2,2,4- and 2,4,4-trimethyladipic acid, azelaic acid, sebacic acid, aliphatic diamines such as hexamethylene diamine, 2,2,4- and 2,4,4-trimethylhexamethylene diamine, the isomeric diaminodicyclohexylmethanes, diaminodicyclohexylpropanes, bis-aminomethylcyclohexane, aminocarboxylic acids such as aminocaproic acid and/or the corresponding lactams. Copolyamides of several of the aforementioned monomers are included.
Particularly preferred are caprolactams, and most particularly preferred is xcex5-caprolactam.
Polyamide 6 and/or polyamide 6,6 are particularly preferably used. Polyamide 6 is most particularly preferably used.
The polyamides produced according to the invention may also be used mixed with other polyamides and/or further polymers.
Commercially available glass fibres, carbon fibres, mineral fibres, fillers with or without surface treatment, etc., for polyamides, are used individually or in mixtures as reinforcing materials B). Preferred fibre-shaped or particle-shaped fillers and reinforcing materials are glass fibres, glass spheres, glass fabrics, glass mats, aramide fibres, carbon fibres, potassium titanate fibres, natural fibres, amorphous silicic acid, magnesium carbonate, barium sulfate, feldspar, mica, silicates, quartz, kaolin, talcum, titanium dioxide, wollastonite, i.a., which may also be surface treated. Particularly preferred reinforcing materials are commercially available glass fibres. The glass fibres, which generally have a fibre diameter of between 8 and 18 xcexcm, may be added as endless fibres or as cut or ground glass fibres, in which connection the fibres may be treated with a suitable sizing system and a coupling agent or coupling agent system, for example based on silane.
As branching additives C) for the moulding compositions according to the invention, there are used for example commercially available diepoxides based on diglycidyl ether (bisphenol A and epichlorohydrin), based on aminoepoxide resins (aniline and epichlorohydrin), based on diglycidyl esters (cycloaliphatic dicarboxylic acids and epichlorohydrin) individually or in mixtures, as well as, preferably, diepoxides based on 2,2-bis[p-hydroyxphenyl]-propane diglycidyl ether, bis-[N-methyl-N-2,3-epoxypropylaminophenyl]-methane.
As component D there may be used conventional additives such as agents against thermal decomposition, agents against thermal crosslinking, agents against damage by UV light, platicisers, lubricants and mould release agents, nucleating agents, stabilisers, as well as dyes and pigments.
Examples of oxidation inhibitors and thermal stabilisers are sterically hindered phenols and/or phosphites, hydroquinones, aromatic secondary amines such as diphenylamines, various substituted members of these groups and their mixtures in concentrations of up to 1 wt. % referred to the weight of the thermoplastic moulding compositions.
As UV stabilisers, which are generally used in amounts of up to 2 wt. % referred to the moulding composition, there may be mentioned various substituted resorcinols, salicylates, benzotriazoles and benzophenones.
Inorganic pigments such as titanium dioxide, ultramarine blue, iron oxide and carbon black, and furthermore organic pigments such as phthalocyanines, quinacridones, perylenes as well as dyes such as anthraquinones may be added as colouring agents, together with other colouring agents.
As nucleating agents there may for example be used sodium phenyl phosphinate, aluminium oxide, silicon dioxide as well as, preferably, talcum.
Lubricants and mould release agents, which are conventionally used in amounts of up to 1 wt %, are preferably ester waxes, pentaerythritol stearate (PETS), long-chain fatty acids (for example stearic acid or behenic acid), their salts (e.g. Ca or Zn stearate) as well as amide derivatives (e.g. ethylene bis-stearylamide) and also low molecular weight polyethylene or polypropylene waxes.
Thermoforming (heat forming) is understood in this patent application to denote a production process in which a thermoplastic film or sheet is heated up to the softening point, is formed at low pressure in a tool, is cooled and then post-treated. All thermoplastic materials that can be produced as films or sheets are in principle also thermoformable, with the proviso that the temperature does not exceed the thermal stability of the material. The inherent strength should be sufficient to prevent an excessive sag resulting in tearing of the film or sheet. The thickness range of freely thermoformable semi-finished products extends from 0.1 mm thick films up to 10 mm thick sheets (Kunststoff Handbuch 3/4 xe2x80x9cPolyamidexe2x80x9d Hanser Verlag, Munich, Vienna, p. 459, 460.
In thermoforming only one side of the heated semi-finished product comes into contact with the forming tool. The surface contours of the forming tool are accurately reproduced on the application side of the semi-finished product. The contour and also the dimensions on the other side of the formed part are governed by the resulting wall thickness of the thermoformed part. In principle a distinction is made between positive and negative forming depending on whether the inside or outside of the formed part is brought into contact with the forming tool. The forming accuracy on the internal contour (positive forming) or on the external contour (negative forming) of the moulding is determined accordingly.
The basic advantages of thermoforming are inexpensive thermoforming tools, cheaper thermoforming machinery, and the possibility of also being able to process multi-layer materials, foamed substances and pre-printed semi-finished products (xe2x80x9cThermoformen in der Praxisxe2x80x9d, Schwarzmann, P., Hanser Verlag, Munich, Vienna, 1997).